This invention relates to the treatment and recycling of waste material, especially waste material which comprises at least some organic matter. More particularly, the invention relates to a method and apparatus for compressively separating such waste material into (a) a liguid or semisolid sludge and (b) solid waste, the sludge containing water together with the organic matter and/or biologically useful materials, and the solid waste being compressed into solid blocks which are cohesive enough to be stored and handled in use, e.g., as fuel briquettes. The extracted sluge may be used as a soil additive.
Machines and methods have already been proposed for separating refuse into liquid or semisolid sludge, on the one hand, and solids substantially devoid of moisture, on the other hand. Commercially available apparatus is at least partially described in French Pat. No. 2,389,577.
However, such prior art machines operate in such a way that the waste material is intensively crushed i.e. a compression piston compresses only part of a mass of refuse contained in a receptacle into a cup shaped mass, then withdraws, whereupon another piston changes the cup-shaped mass produced by the first piston into a cake-shaped mass, into which the first piston returns to compress a new indentation, etc. Hence part of the mass, facing the end of a cylindrical compression piston, is compressed at high pressure, whereas the rest of the mass at the sides of said piston are hardly affected by its action. As a matter of fact, waste materials of all kinds do not behave in accordance with the laws of hydrostatics (which would give the same pressure at all locations), nor do they behave in accordance with the laws of the mechanics of rigid bodies, where the forces are calculated without taking the effects of creep or flow into account. Instead, the laws which govern the phenomenon of compression of a mass of refuse are those of soil mechanics, the principles and details of which are expounded, for instance, in Soils and Soil Engineering, by R. H. Karol, Englewood Cliffs, N.J., Prentice-Hall, 1960.
The science of soil mechanics covers various situations, one being the distribution of pressure in soil of theoretically infinite volume, and another being the distribution of pressure in soil assumed to be confined within rigid walls. The fields of isobaric curves, applied to pistons operating according to the particular concept to be proposed here, are of the shapes shown, for example, in FIGS. 1 and 2 of the accompanying drawings. Also of interest in this connection is FIG. 13.3 on page 127 of the aforementioned Karol text.
The present invention is based on the recognition that if all the liquid, semisolid, or viscous material is to be extracted from a mass of waste material, the apparatus used must be designed to create, at least to a certain extent, a homogeneous pressure within the mass of waste. The prior art apparatus referred to above does not meet this requirement, at least not when the compression piston is first forced into a mass of material to be treated. This first operation, as described above, gives the mass the shape of a cup, the bottom of which is highly compressed but the sides of which are hardly compressed at all, and an intermediate operation for reshaping the mass into a cake-shaped mass is therefore necessary, after which another compression takes place, etc. The result of these reshaping operations is to crush the mass and thereby prevent it from retaining a desired cohesiveness and tenacity. Hence the blocks produced by the prior art machines are very brittle and apt to crumble. Moreover, in the prior art machines, the liquid or semisolid sludge (sometimes also referred to as the liquid phase) escapes through grooves disposed along the compression piston. Hence the sludge starts to escape as soon as compression is exerted, and there is no preparatory compression phase without sludge withdrawal. This also seems to contribute toward making the blocks of solid waste more friable, and the solid waste cannot therefore be used as fuel except in the form of the small scraps into which the blocks disintegrate when stored or otherwise handled.
Other arrangements of the same kind are proposed in French Pat. No. 487,552, No. 419,408, and No. 617,721. However, none of these prior disclosures contemplates a separation technique by compression in accordance with the principles of soil mechanics.